We are not aware of any studies published on the effect of aromatase inhibitors in dogs with mammary carcinoma, but based on the fact that many of these tumors are estrogen-dependent, express estrogen receptors, and respond to tamoxifen, it is reasonable to believe that aromatase inhibitors should be effective.

Aromatase inhibitors prevent estrogen synthesis, whereas tamoxifen works by blocking the estrogen receptor. Oophorectomy ("spaying" your dog) ablates the major source of estrogen production. The goal of all of these hormonal therapies is to help prevent mammary carcinoma cells from receiving further stimulation from estrogen.

Unfortunately we cannot provide any information about a specific aromatase drug, its dose, or its effectiveness, since its use is theoretical and no actual canine studies on this have been reported. If the dog is intact, then spaying would be a reasonable, more established approach.

Feb 12, 2010 - The overexpression of low-molecular-weight cyclin E in the tumors of many menopausal women with estrogen-receptor-positive breast cancers nullifies the effects of letrozole, an aromatase inhibitor. However, letrozole's effect can be restored by adding the cyclin-dependent kinase 2 inhibitor roscovitine to treatment, according to a study published online Feb. 9 in Clinical Cancer Research.